Ben & Jerry's co-founder Ben Cohen thinks money shouldn't be used to "bribe" politicians, but he's doing a little bribing of his own when he hits D.C. next month. Cohen and his "Stamp Stampede" are headed to Union Station on June 18, starting at noon, and giving out free ice cream -- with a catch.

To raise awareness about a proposed constitutional amendment that would fund federal elections using public money, Cohen is asking that folks stamp their dollar bills with phrases like "Not To Be Used for Bribing Politicians" and "Stamp out Money in Politics." (His lawyer says this is perfectly legal).

This "petition on steroids," as it's being called, could reach an average of 875 people per stamped dollar bill. A stamping station will be set up on Union Station's West Porch until 3 p.m., and everyone who presents a stamped dollar will get free Ben & Jerry's ice cream.